1. Technical Field
This invention relates to imaging media having at least one antihalation layer associated therewith. The antihalation layer is translucent and is rendered transparent by the application of heat and/or pressure
2. Background Art
There are many potentially adverse phenomena which can occur during the imaging and development of photosensitive media. One of these adverse phenomena is named halation. The source of this problem has been long recognized as the reflection of light from the back of the photosensitive media. The reflected light is diffuse, and when high intensity radiation is used in the exposure step, a sharp halo of light is produced which generates an undesirable image in the media Many types of radiation absorbing layers have been placed on photosensitive media to absorb the radiation before it is reflected These radiation absorbing layers are termed antihalation layers.
One problem with the use of antihalation layers is that in order for them to absorb radiation to which the photosensitive media is sensitive, the layers must often absorb visible radiation. This renders the antihalation layers visible and the layers can interfere with the viewability of the desired image. It is therefore an essential characteristic of most antihalation layers that any visible characteristics of the antihalation layer are removable at some point after exposure, usually during or after image development.
In silver halide photographic materials, aqueous alkaline soluble antihalation layers containing carbon black are used on the backside of the photographic media. These antihalation layers are dissolved and removed during development of the photographic media. Such antihalation layers are shown in U.S. Pat. Nos. 2,271,234; 3,392,022; 4,039,333 and 4,262,088.
Vesicular imaging films and diazo imaging films are also known to utilize antihalation layers as reported in U.S. Pat. No. 3,466,172. Here, an antihalation layer of actinic radiation absorbing diazo compounds is deactivated by post-exposure of the antihalation layer to actinic radiation.
The use of bleachable dye-containing layers as antihalation layers is also known in the art. The dyes may be chemically bleachable (e.g., U.S. Pat. Nos. 3,769,019 and 4,336,323) or heat bleachable (e.g., U.S. Pat. Nos 4,196,002 and 4,316,984).
Other antihalation layers have been described which are physically stripped from the imageable material after image development (e.g., U.S. Pat. No. 4,262,088).
Each of these systems provide improved halation characteristics to the imaging media, but also provide some attendant problems Antihalation layers which are removed in development baths tend to foul up the baths with binders and pigments. It is often difficult to find dyes which are both bleachable and absorptive at the desired wavelengths. Bleachable dyes tend to leave color residues or stains in the image. It is therefore desirable to find antihalation layers which have a broad range of spectral absorptivity and which are readily converted to a lower radiation absorptive activity after imaging.